- Firmware version: Any
- Model: S-Series
Two extensions are registered to Yeastar S-Series PBX. Extension 13 comes from an N510 IP Phone and extension 14 comes from Cisco SPA122. When extension 13 calls extension 14, the call can not be established and 13 hears the busy tone. Meantime, calls work like a charm when 14 is registered on a soft or IP phone.
A brief introduction of Cisco SPA122:
Cisco SPA122 is short for Cisco SPA122 ATA with Router. It could register two SIP extension accounts at most.
But actually, two analogue devices, such as analogue phones and fax machines, are associated with them through its physical ports.
For more info about Cisco SPA122, please refer to this guide: https://www.cisco.com/c/dam/en/us/products/se/loc/datasheet_C78-691107.pdf
The attached PCAP log shows Cisco SPA122 requires to authorize INVITE from S-Series PBX, unlike the normal call flows. So the issue needs to be resolved in Cisco SPA122.
Disable Auth INVITE in Cisco SPA122 and then it should work.